Most frequently, fast neutron nuclear reactors cooled by a liquid metal, which represents the primary fluid of the reactor, comprise intermediate heat exchangers, in which the heating of a liquid metal is brought about, this liquid metal representing the intermediate fluid, which is used, in turn, for the vaporization of the feed water in the steam generators.
These steam generators possess a cylindrical envelope, having a vertical shaft and being closed by convex ends, inside which the tube bundle is located. This bundle, generally consisting of spirally wound tubes, occupies only part of the cross-section of the internal volume of the envelope and extends over only part of the height of the envelope.
Above the bundle there is a zone into which issues at least one inlet pipe for secondary liquid sodium heated by the primary sodium in an intermediate exchanger, while the lower part of the steam generator is provided with an outlet pipe for the cooled secondary liquid sodium.
Between its entry and its exit from the envelope of the steam generator, the secondary liquid sodium circulates in contact with the external surface of the tubes of the tube bundle, inside which feed water circulates, and is vaporized by heat exchange with the secondary liquid sodium.
One end of the tubes of the bundle is connected to a water-feed device, while the other end of the tubes of the bundle is connected to a steam-collector device.
During its downward passage in contact with the tube bundle, the secondary liquid sodium is cooled. This cooled sodium is returned to the intermediate exchangers to be heated and to cool the primary sodium.
In the steam generators of the fast neutron nuclear reactors currently built, the central part of the internal volume of the envelope is taken up by a cylindrical central body, co-axial with the envelope of the steam generator, from the lower part of the steam generator to the upper zone where the secondary liquid sodium enters. The tube bundle takes up the peripheral part of the internal volume of the envelope, around the central body and over the entire height of the latter, with the exception of its lower part, in which apertures enable secondary liquid sodium to be recovered after passing through the bundle.
The feed of secondary sodium and the circulation of the latter in the steam generator are regulated so that the top level of this secondary sodium in the envelope of the generator is located slightly above the sodium inlet, in the upper part of the envelope.
The space between the top level of the sodium and the top end of the steam generator is filled by an inert gas, such as argon.
In the case of water leaking onto one of the tubes of the tube bundle, a violent reaction takes place between the liquid sodium and the water and a pressure wave passes through the steam generator from the place where the leak appeared to the liquid sodium/inert gas interface where this pressure wave is reflected and its pressure is gradually released.
These pressure waves can damage not only the heat exchanger, but also the various components of the secondary sodium circuit.
It is therefore necessary to promote the propagation of the pressure waves towards the free level of the liquid sodium where these waves are absorbed.
Moreover, the passage of the pressure wave through the steam generator to the free level of the liquid sodium is generally very long, whereas it would be desirable for these pressure waves to reach a free surface as quickly as possible.
To date, simple apparatus, was known which, though occupying little space, enabled the pressure waves which can arise in a steam generator containing liquid metal to be absorbed very rapidly.
The object of the invention, therefore, is to propose an apparatus for the production of steam by heat exchange between a heat-transfer liquid metal and feed water, this apparatus possessing a cylindrical envelope, having a vertical shaft and being closed by solid ends, inside which a tube bundle is located which occupies only part of the cross-section of the internal volume of the envelope, over only part of the height of this envelope, at least one pipe for introducing heat-transfer liquid metal into the envelope, passing through the latter into a zone located above the tube bundle, at least one outlet pipe for the liquid metal, passing through the envelope in its lower part, means for feeding the tubes of the bundle with feed water, and means for the recovery of the steam produced in the tube bundle by heat exchange between the liquid metal, circulating in contact with the surface of the tubes of the bundle, and the feed water, the top level of the liquid metal having above it an inert gas which fills the top part of the envelope and this apparatus, enabling rapid absorption of the pressure waves which can arise in the case of water leakage in the tube bundle, wherever the leak may be.
To this end, at least two compartments are constructed inside the envelope in a zone that is not taken up by the tube bundle, located above one another and delimited by walls creating a passage for the liquid metal between the compartment and the internal volume of the envelope, in the lower part of each compartment, each of the compartments being placed in communication with the compartment located directly above by means of an approximately vertical first tube, and with the compartment located directly below by means of an approximately vertical second tube, both tubes issuing at a certain height into the compartment under consideration, so that the end of the second tube is above the end of the first tube, the compartment, located at the highest level in the envelope communicating with the upper part of the envelope filled with inert gas, while the compartment located at the lowest level is in communication with a reserve of inert gas for establishing liquid metal/inert gas interfaces in each of the successive compartments, through the introduction of inert gas from the compartment located at the lowest level.
For a complete understanding of the invention, an embodiment of a steam generator of a fast neutron nuclear reactor cooled by means of liquid sodium and comprising several liquid sodium/inert gas interfaces will now be described, with reference to the attached drawings.